The present application relates to a display device which includes a display surface and which can display information such as an image or characters on the display surface, and more particularly to a display device which can detect an object to be detected either contacting or approaching a display surface.
A liquid crystal display device, an organic EL (electroluminescence) display device, and a display device utilizing an electrophoresis method are known as display devices each capable of displaying thereon information such as an image or characters.
Along with the promotion of the thinning of the display devices, numerous functions having a function of an input unit or the like for inputting therethrough an instruction or the like from a user as well as an original function of displaying an image, characters or the like are required for the display devices. A display device capable of detecting that a finger of a user or a stylus pen (a so-called touch pen or the like) manipulated by the user either contacts or approaches a display screen is known as a display device which responds to this requirement.
The detection of contact can be carried out with a touch panel utilizing either a resistor film system or an electrostatic capacitance system. Also, there is known a display device having a touch panel which is added to a display surface side of a display panel such as a liquid crystal panel.
However, the addition of the touch panel to the display surface side of the display panel is disadvantageous in the promotion of the thinning of the display panel, and triggers cost-up of the display device. In particular, in the case of the touch panel utilizing the resistor film system, no change in resistance value of the resistor film can be detected unless the screen is depressed with certain degree of a strength. For this reason, the display surface is deformed. In addition, the general principle of the touch panel utilizing the resistor film system is one point detection. Thus, use application of the touch panel is limited.
A display device having an optical position detecting function, and a light receiving element built in a display panel for detecting an indicated position is known as a display device, utilizing an indicated position detecting system, which requires no touch panel. This display device, for example, is described in Japanese Patent Laid-Open Nos. 2005-275644 and 2006-301864.
In the optical position detection, a system for detecting a shadow of a finger or the like of a human being based on a quantity of outside light received is generally used. In the case where there is an object (such as a finger of a human being, or a stylus pen manipulated by the human being which will be referred hereinafter to as “an object to be detected”) when the outside light is made incident to the display surface, a level of an output signal from a light receiving element for detecting the outside light is low due to the presence of a shadow of the object to be detected. Thus, a position of the object to be detected is identified based on the output signal from the light receiving element.
On the other hand, the display device described in Japanese Patent Laid-Open No. 2006-301864 has a light receiving element (hereinafter referred to as “an optical sensor”), having sensitivity to a nonvisible light, which is provided inside a liquid crystal (or organic EL) display panel.
In the case of the liquid crystal display panel, a backlight is disposed on one principal surface (back surface) side of the liquid crystal display panel. Lights from the backlight contain therein a visible light component and a nonvisible light component. The lights from the backlight suffer the modulation corresponding to an input video signal in a liquid crystal layer when being transmitted through the liquid crystal display panel to be emitted from the other principal surface (a front surface or a display surface). The visible light component of the emitted lights is modulated, thereby displaying a predetermined image on the display surface.
When there exists an object (an object to be detected) either contacting or approaching the display surface side of the liquid crystal display panel, a part of the emitted lights is reflected by the object to be detected to become a reflected light which is in turn guided to the optical sensor side. The optical sensor detects especially the nonvisible light component of the reflected light from the object to be detected. A visible light cutting (non visible light selecting) filter is provided so as to correspond to an area having the optical sensor provided therein. Also, in this area, no transmitted light suffers the modulation corresponding to the video signal. For this reason, the object to be detected can be detected without being influenced by the display state, and without being influenced by a degree of an environmental brightness. A large number of optical sensors are disposed regularly (discretely and two-dimensionally), which results in that it is possible to detect a position and a size of the object to be detected.
The organic EL display device requires no backlight, and a pixel itself emits a light. In this case, light emitting elements for emitting nonvisible lights, and light receiving elements for receiving the nonvisible lights are disposed at predetermined intervals within a display area of a panel. A method itself of detecting the object to be detected is similar to that in the case of the liquid crystal display device described above. The nonvisible lights emitted from the light emitting elements are reflected by the object to be detected. Also, differences in quantities of reflected lights are detected by a plurality of light receiving elements which are disposed discretely, two-dimensionally, thereby making it possible to detect a position and a size of the object to be detected.
In the display device described in Japanese Patent Laid-Open No. 2005-2756644, an optical sensor is disposed on a backlight side of a spacer through which the liquid crystal layer is separated so as to correspond to the pixels. An area in which a light receiving element having sensitivity to the visible light (hereinafter referred to as “a visible light sensor”) is disposed, and an area in which an applied voltage to the liquid crystal layer can be changed so as to correspond to a video signal, and thus the transmitted light can be modulated (hereinafter referred to as “a light modulation area”) are both provided in an area within the pixel different from the dispersion area of the optical sensor.
In the display device described in Japanese Patent Laid-Open No. 2005-275644, the lights reflected by the object to be detected such as the finger of the human being, or the stylus pen manipulated by the human being can be detected based on both the nonvisible light and the visible light.
According to the techniques described in Japanese Patent Laid-Open Nos. 2005-275644 and 2006-301864, the object to be detected by using the nonvolatile light which does not exert an influence on the displayed image because it is invisible for the human being. Therefore, when a quantity of transmitted light, of the visible light, passing from a back surface to a front surface is approximately near zero as in the case of the black picture display, the object to be detected can be detected at the time as well of the black display because even when the nonvisible light is transmitted to the front surface side, no influence is exerted on the display. Thus, the object can be detected irrespective of that the circumference is either dark or bright.